Recent years have seen an explosion of interest in gourmet coffee products and the interest has not been limited to the purchase of coffee-based beverages from vendors who prepare the beverage on premise and purvey it to consumers over the counter. The desire is now for the ultimate in freshness and flavor and that is roasting the coffee on site at the coffee shop and or at home. Coffee roasting is a two-step process. The outside of a bean is covered with a husk which also follows a fold into the center of the bean. As it is roasted, the coffee bean expands and literally “pops” to shed the outer husk. If the bean is properly roasted, the center of the bean further expands and allows some of the internal husk to break free of the bean.
Currently coffee beans are roasted via two common methods and a third one that is less common. The common methods are convection and conduction. Convection uses a heated air steam to heat the bean and “float” it in an air stream to reduce burning; however, this heated air system also strips away through evaporation a large amount of the coffee oils that are vital components in the flavor of superior coffee. Conduction is the other roasting method and in this system only heat from the externally heated open metal drum is used to roast the bean through direct contact The conduction method rotates the drum for agitation to prevent scorching the coffee bean. The conduction system still uses air that is circulated in the drum to remove heat and smoke and results in loss of lighter coffee oils (and their flavor) just as in the convection system. The conduction system also prevents the controlled and easy transfer of the heat to penetrate the husk and cause the internal mass of the bean to quickly rise to a desired temperature. This causes moisture and oil within the bean to vaporize and expand, thereby applying pressure to the husk and resulting in the popping of the bean. The mass of the bean expands and the husk is freed from the bean. The other method of roasting beans is the use of steam as shown in U.S. Pat. No. 5,681,607, issued on Oct. 28, 1997 to Maki, et al. Roasting with superheated steam, however, tends to make the coffee much more sour. The steam process use a high-pressure vessel and high steam temperatures and pressures making this system potentially very dangerous for the home and commercial user. The steam system alone cannot provide the dark and very dark roasts that are desired by most of the coffee drinking public. Various embodiments of the invention use “latent” steam in combination with convection, conduction, infrared, and microwave heating to provide a full spectrum of roasting levels. Latent steam is a result of the water that is contained in the coffee beans (generally 10%-12% by weight) and is boiled out of the bean during the initial convection/conduction/microwave heating that is part of the roasting process. This latent steam is a contributor to making the coffee more “mellow,” as in the steam-only process; but because it is part of the bean, it requires no separate boiler and due to the design of the cartridge is of low pressure and thereby is not a hazard.
Other problems with conductive, convection and steam roasting include a situation where a bean is roasted at too low of a temperature, the moisture build-up is sufficiently slowed as to allow the vapor to escape without building up sufficient pressure to pop the bean. When this occurs, the bean will be of smaller size than if proper roasting occurs and has a green grassy flavor. On the other hand, if a bean is roasted at too high of a temperature, the bean will be burned, i.e., overly caramelized, and taste will suffer. In some cases, high temperature roasting will result in a burning of the husk. As the husk serves as a moisture barrier to allow pressure to build up during roasting, the burning of the husk destroys the moisture barrier and allows the moisture to escape without building up sufficient pressure to pop the bean. The second stage of roasting occurs once the bean pops. Here, the heating of the oil within the bean results in chemical changes to roast the bean to the taste of a particular consumer. In many instances, continued roasting of the bean after popping causes a further expansion of the bean. To achieve optimum roasting, it is necessary that the beans be uniformly heated internally via microwaves and externally via conduction, convection and latent steam while not allowing any of the oils and essences that are components of the flavor to escape into the air prior to grinding. If the heating is not uniform, some of the beans may pop early in the roasting process and others, not at all. Consequently, uniform flavor cannot be obtained. Similarly, it is necessary that roasting temperature be properly controlled to assure proper flavor development which cannot occur if the roasting temperature is either too low or too high.
Other common problems with current coffee roasters is the issue of smoke and excessive aroma. The smoke and excessive aroma is dealt with on existing commercial roasters by the use of stack scrubbers and after burners, the problem is dealt with on home coffee roasters by there recommend use out doors. Other problems that the current roasters have is high energy cost per pound of beans either using gas or electricity. This is on the order of 50% higher than microwave driven roasting. The present invention is directed to overcoming one or more of the above problems.